ES2989689T3 - Quality control method for regulating the operation of an electromechanical device, for example, an EBM device, in order to obtain certified processed products. - Google Patents

Abstract

The invention relates to a method for regulating the operation of an electromechanical apparatus (1), for example an EBM apparatus, in order to obtain certified processed products, in which an initial calibration step is provided for checking the correct operation of all the components of the apparatus (1) structured to ensure full functionality and a subsequent quality control step performed on the products obtained by the work process performed. The method involves the following steps: - defining a plurality of measurement parameters related to the components of the apparatus; - measuring at least some of said parameters by means of sensors and/or measurement indicators related to said parameters during at least one processing phase performed by the apparatus; - performing a quality control step on the products obtained after the work process by obtaining data on any deviation from the expected quality; - comparing the detected measurements of said parameters and the data on any deviation from the expected quality with the corresponding values of the reference parameters available for that specific apparatus and for those products; - detecting any deviation in one or more of said parameters or said data from the values of the reference parameters; - calculating, from said differences, a total correction and regulation value; - applying said total correction and regulation value preferably to only one of said parameters before the subsequent process, for example to the energy of generation of the electron beam (3). Basically, the method of the present invention allows to obtain semi-finished products free of structural defects by means of a primary check of the correct functioning of the various components of the apparatus (calibration procedure), a secondary check of the operational efficiency of the process itself (operational qualification procedure) and a further final check of the stability and repeatability of the process within a process window (performance qualification). (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Quality control method for regulating the operation of an electromechanical device, for example, an EBM device, in order to obtain certified processed products.

Scope

The present invention relates to a method for regulating the operation of an electromechanical apparatus, which is an EBM apparatus, in order to obtain certified processed products.

More particularly, the invention relates to the field of additive manufacturing techniques and technologies. More specifically, the present invention falls within the scope of manufacturing three-dimensional objects starting from computerized 3D models, in the field of additive manufacturing using Electron Beam Melting (EBM) technology.

Even more particularly, the invention relates to a method of validating the EBM process to allow qualifying and certifying the correct functionality of an EBM apparatus or system and of the related products obtained therewith.

Prior art

EBM (Electron Beam Melting) technology makes it possible to create semi-finished objects or components directly from metal powders using a focused electron beam according to the principles of additive manufacturing technologies (also called “additive manufacturing”). This technology is described for example in PCT patent application No. WO2011/008143 by the Swedish company Arcam. EBM devices generally have a high voltage unit feeding an electron gun adapted to generate an electron beam that is transported inside a working chamber. The entire assembly is controlled by suitable programmable means. EBM technology uses this electron beam to sinter a predetermined quantity of powder that is extracted from dedicated deposits and distributed in a working area of the EBM device.

Inside the working chamber, the production process involves placing the powder layers of the material to be melted in a vacuum. Working in a vacuum also makes it possible to work on materials that would otherwise react immediately with the oxygen in the air, thus producing undesirable compounds.

The process implemented within an EBM device includes three steps, which can be outlined as follows:

1. A first entry step comprising:

Enter or load files about the components to be manufactured to activate the programmable means dedicated to the manufacture of the products;

Insert the metal powders into the working chamber.

2. A second fusion step, which involves: - Adjusting the configuration and control parameters of the software and hardware components of the EBM apparatus;

Form vacuum in the melting chamber;

Real EBM fusion;

3. A third, final output step, which produces the finished product. The configuration of the machine is of primary importance, both in terms of hardware components and in terms of software applications that regulate the execution of the process.

In order to better understand the aspects of the present invention, it is important to keep in mind that the electrons of the electron gun are produced by feeding a tungsten filament with a high potential, generated by a high voltage unit (HV unit). Furthermore, in order to be effective, it is necessary that the electron beam be generated under conditions of absolute vacuum, in order to avoid phenomena of interaction of the electrons with the molecules of the atmosphere.

It is also essential that these conditions can be maintained with stability in order to allow the correct execution of the fusion process and to repeat subsequent fusion processes with a guarantee of quality and stability in production.

More specifically, the stability of the process is guaranteed by certain fundamental parameters: a) the filament current, which quantifies the kinetic energy of the emitted electrons and the consequent power/speed of the electron beam; b) the degree of vacuum of the electron beam generation environment, both in the electron gun and in the fusion chamber; c) the movement of the collector/distributor, i.e. the device intended to collect and distribute the correct quantity of powder, in order to obtain a uniform layer for the fusion step; d) the composition or theme, i.e. the set of information containing the configuration and management parameters of the electron beam that regulates the energy of the electron beam according to the operations to be performed using the electron beam; these operations include, for each powder layer fusion process, the following steps:

- powder heating,

- contour fusion,

- solid parts,

- network structures.

e) movement of the moving tray, which descends to ensure the development and production of the sintered products;

f) temperature of the platform or work plate (called start plate), constantly measured to check that the melting temperature of the powders is constant and leads to the generation of a uniform fusion from the microstructural point of view. In fact, the correct operation of the electron beam is controlled and regulated by reading the temperature of the start plate.

The EBM process is completed using some auxiliary units necessary for the recirculation and reuse of raw material (i.e. powders), and for the post-process treatment of the sintered products and components (e.g. cleaning them from unaggregated powders). The EBM apparatus is provided with some important auxiliary components, such as a so-called Controlled Vacuum (CV) apparatus that regulates the vacuum level by the controlled introduction of small amounts of inert gas into the chamber, and an interface application software that ensures the integration and operation of all the machine parts. It is evident that an EBM apparatus is a complex electromechanical system in which there are auxiliary units necessary for the movement of the system components and the raw material (powders), as well as for the further processing of the manufactured products and for the maintenance of the entire apparatus.

For example, the measurement of the amount of powder distributed in step (c) is controlled by reading two sensors placed on the sides of the start plate.

Instead, as part of step (d), the parameters of the composition or filament are responsible for adjusting the energy that the electron beam must have in order to optimize the fusion process, for example in terms of electron beam speed or current flow to be delivered to the filament. In fact, for the fusion process to be optimal and to allow maximum flexibility in terms of the geometries that can be made, the electron beam flow must be precisely modulable only within predetermined areas for the realization of particular fusion lines.

The electron beam movement and modulation operations are carried out through the use of magnetic coils placed on the sides of the column that transport the electrons to the EBM chamber.

Also as regards steps (e) and (f), in order to achieve the desired geometries of the products to be sintered, in addition to properly moving the electron beam and modulating its energy to allow a correct energy transfer to the powder, the temperature of the molten layer should be kept constant to achieve uniform products from the point of view of their structural density and their physical-chemical-mechanical properties.

Furthermore, the volume of the material to be melted also affects the density and characteristics of the products obtained, and different volumes to be melted require different energies. That is why the correct amount of powder distributed on the starting plate must also be controlled and kept constant.

Obviously, the EBM equipment manufacturer provides the basic reference specifications that illustrate how to perform the operations from the beginning of the process to continue with post-processing and system maintenance; all in a dedicated manual and with training courses.

Currently, EBM systems have the CE marking required, like any other product, for their introduction into the European market. This CE certification process involves an installation procedure and a machine qualification. However, although the functionality of the system is initially guaranteed by the manufacturer and verified at the first installation, a qualification and certification of the functionality of the EBM process during operations, i.e. during many processing steps carried out each time, is completely missing. The impact of a malfunction of one or more parts of the system cannot currently be discerned, even a posteriori by third parties; furthermore, some control procedures for parts of the system are sometimes missing from the documentation provided by the manufacturer and the consequences of an incorrect calibration or configuration of the system in terms of the acceptability of the produced material, i.e. absence of defects and/or the correct manufacture of the designed product, are also unknown.

The above deficiencies can lead to some process deviations during the actual melting step which, if not properly calibrated using costly and repeated verification testing and machine adjustments, can result in the creation of non-conforming products.

Deficiencies in process functionality control can lead to the following effects:

- high percentage of waste in production;

- increased costs and manufacturing times;

- the need for frequent and constant monitoring of all sintered products; this monitoring is also often difficult and laborious due to the extreme constructive freedom allowed by EBM systems;

- need to adopt EBM post-melt recovery treatments capable of mitigating some manufacturing defects, such as HIP (Hot Isostatic Pressing).

All this represents a major drawback in terms of the productivity that can be obtained with this manufacturing technology, but also for its applicability in areas where respecting production quality is of fundamental importance (for example in the medical, aerospace, etc. fields).

In order to limit the consequences of these inconveniences, the EBM system manufacturer has only provided an initial device validation protocol, linking them to a specific set of machine configurations.

Although in many ways advantageous and likely to improve the quality of the process in terms of good quality of manufactured products, these expedients suggested by the manufacturer do not allow to remedy deviations of EBM systems.

Paradoxically, verifications of the correct calibration and configuration of the parameters of the device and its component parts are also subject to deviations to the point that these deviations affect the quality of the products obtained, especially in the medical field.

Therefore, at present, these aspects remain undefined and the know-how underlying some operating steps of the apparatus is unknown, for example: the connection between the change of parameters and the technical effect on the machine and on the produced material is not yet formalized for the user of the apparatus. The prior art proposes a solution, described in US patent application No. US 2015/017054, to try to improve the quality of the production obtainable by means of an EMB apparatus over time. However, this solution is limited to measuring eddy currents in the product under development as the only quality control parameter, but does not check the operating parameters of the apparatus itself.

The technical problem to be solved is to devise a method for regulating the operation of an electromechanical apparatus, of which all individual structural and functional aspects of calibration are not known in detail, for example, an EBM apparatus, in order to obtain certified processed products.

The method in question should have such functional characteristics as to allow the validation of the EBM fusion process in order to qualify and certify its functionality in a simple, effective, efficient and reliable manner, with a high degree of security.

Another object of the invention should be to cover any knowledge gaps concerning the effects of calibration and process parameters of the apparatus that allows manufacturing three-dimensional products through EBM technology.

The known art proposes a solution to improve over time the quality of the production that can be obtained by means of an EBM apparatus. Such a solution is described in US patent application No. US 2015/017054. However, that solution is limited to detecting eddy currents inside the product under construction as a single parameter to detect the final quality and does not care to check other operating parameters of the apparatus itself.

ASTM F3055:14a (2014) describes a Standard Specification for Additive Manufacturing of Nickel Alloy (UNS N07718) Using Powder Bed Fusion.

Patent document US2015/017054A1 relates to a method for generatively producing components by layer-by-layer construction from a powder material through selective material bonding of powder particles using a high-energy beam.

The paper “Mechanical Properties of Laser Beam Melting Components Depending on Various Process Errors” by Kleszczynski et al. (2013) relates to a Laser Beam Melting process for the production of metallic components, where process errors are identified and documented using high-resolution imaging.

The document “Standardization in additive manufacturing: activities carried out by international organizations and projects” by Monzón et al. (2014) presents a summary and review of the actions carried out with the aim of developing new standards in Additive Manufacturing.

The paper “Influence of selected parameters of Selective Laser Sintering process on properties of sintered materials” by Stwora et al. (2013) refers to an investigation on the influence of Selective Laser Sintering (SLS) parameters such as: laser power, spot distance, scanning speed and exposure time on the density and compressive strength of the sintered material.

Patent document US6580959B1 refers to a method for remotely controlling the manufacture of a product by depositing successive layers of material through a local direct material deposition system controlled by feedback and assisted by laser.

Patent document EP2620240A1 relates to the formation of an aerodynamic profile in deposited layers of material.

Patent document US2014/061167A1 relates to the fabrication of electron beam layers using a closed loop control monitored by scanning electrons.

The paper “Microstructure, Texture and Mechanical Property Evolution during Additive Manufacturing of Ti6AL4V Alloy for Aerospace Applications” by Alphons Antonysamy (2012) investigates the influence of processing conditions on microstructure and texture evolution and its resulting effect on mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, i.e.; 1) Selective Laser Melting (SLM) process, 2) Electron Beam Selective Melting (EBSM) process and, 3) Wire Arc Additive Manufacturing (WAAM) process.

Patent document US2013/055568A1 relates to a method for manufacturing a layered component of powdered component material, the method comprising locally melting and/or sintering layers of the component material by supplying energy with the aid of at least one electron beam, wherein material information, characterizing the topography of the melted and/or sintered component material, is determined on the basis of the emitted electrons.

In summary, the problem underlying the invention is to devise a method of the above type and adapted to allow a validation of the EBM process by providing control procedures of all the component parts of the apparatus, defining a correct calibration and adjustment of the apparatus itself and evaluating the impact of a possible malfunction of one or more parts, taking corrective actions and thus avoiding deviation of the EBM process.

Compendium of invention

The solution idea underlying the present invention is to find a method for regulating the operation of an electromechanical apparatus, such as an EBM apparatus, in order to obtain certified processed products, of the type where an initial calibration step is provided, intended to check the correct operation of all the component parts of the adapted apparatus to ensure the full functionality thereof, and a subsequent quality control step carried out on the products obtained by the work process carried out; the results of the quality control of the products obtained provide information about possible deviations from the predefined process parameters and operationally actions are taken by preferably changing a single related parameter that allows to restore the quality of the production to the desired and expected specifications.

Based on the above solution idea, the technical problem is solved by a method for regulating the operation of an EBM apparatus for obtaining certified processed products, according to claim 1.

Therefore, the invention is defined by claim 1 and the preferred embodiments are defined by the dependent claims.

The method comprises:

- defining a plurality of measurement parameters in relation to said component parts of the apparatus;

- measuring at least some of said parameters by means of sensors and/or measurement indicators coupled to an apparatus control unit and related to said parameters during at least one processing phase performed by said apparatus;

- perform a quality control step on the products obtained after the work process by obtaining data on any deviation from the expected quality;

- compare the detected measurements of those parameters and data on any deviation from the expected quality with the corresponding values of the reference parameters available for that specific apparatus and for those products;

- detect any deviation in one or more of said parameters or said data from reference values;

- calculate, on the basis of such differences, a total correction and regulation value;

- apply said total correction and regulation value to the electron beam generating energy of said EBM apparatus or to other parts of the system.

The electron beam generation energy is obtained from formulas for correlating the parameters associated with the component parts of the apparatus, such as:

where:

T is the temperature of the molten layer;

E is the energy applied to the electron beam;

A is the fusion area;

t is the fusion time;

I is the electron beam correlation filament current; and

V the potential across the filament.

Furthermore, the apparatus control unit is capable of calculating on the basis of said formulas, and by means of an automated procedure, the type of energy to be applied to the electron beam to produce processed products corresponding to a predetermined quality level.

Regulation of the electron beam generation energy is accomplished by regulating the current applied to the filament of an electron beam generating gun.

Basically, the method of the present invention allows to obtain semi-finished products free of structural defects by means of a primary check of the correct functioning of the various component parts of the apparatus (calibration procedure), a secondary check of the operational effectiveness of the process itself (operational qualification procedure) based on a specific quality control of the products obtained. A further final check of the stability and repeatability of the process within a process window is provided (performance qualification).

Any correction or corrective compensation of process drifts is preferably carried out by changing a single related parameter which, in this case, is represented by the application energy of the electron beam of the EBM apparatus.

If the results of the checks indicate that only a specific parameter has a drift, for example, a parameter related to a structural and mechanical part of the device, it is possible to intervene only on that structural part with a direct recalibration.

In this way, the productivity of the EBM system is significantly improved in terms of reduction of non-compliances due to incorrect adjustments and/or calibrations of the system, with the consequent decrease in production costs, a process window is defined within which the fundamental characteristics of the manufactured material are respected and not changed, and the process and production of components using this technology is made certifiable according to current regulations, for example in the field of quality in the medical field.

The invention comprises additional and optional features, taken individually or in combination, if necessary.

According to the invention defined by claim 1, the step of defining the plurality of measurement parameters in relation to the component parts of the apparatus is modified with the progress of the useful life of the apparatus and also after the application of said total correction and regulation value.

Furthermore, the step of measuring said parameters provides quality control of the products obtained by means of said at least one processing carried out.

Such quality control includes at least the following tests on product samples obtained from processing:

- Proof of the dimensional correspondence L;

- Tensile tests in the z direction;

- Tensile tests in the x and y directions;

- Complete chemical analysis;

- Evaluation of porosity, discontinuities or micrography;

- Visual, adhesive and compression analysis of the structural network.

It should also be noted that the measurement phase of at least some of the parameters is carried out by means of sensors and/or measurement indicators mounted on the same device.

Furthermore, the comparison of measurements taken from these parameters with the corresponding values of the reference parameters is carried out automatically by an application residing in the command and control unit of said device.

The measurements of these parameters and the values of the reference parameters are stored in a memory section associated with the control and command unit of the device.

Additional features and advantages of the EBM process validation method according to the present invention will become apparent from the following description, given by way of example only with reference to the accompanying drawings.

Brief description of the drawings.

Figure 1 shows a schematic block view of an electromechanical apparatus, such as an EBM apparatus; Figure 2 shows a flow diagram schematically illustrating the different steps of a melting process implemented by the EBM apparatus in Figure 1;

Figure 3 shows a schematic diagram illustrating an energy balance of an operational step of the EBM process to which the method of the present invention is applied.

Detailed description

While a particular embodiment of the present invention is described hereinafter as represented in the relevant figures, it should be noted that the invention is not limited to that particular embodiment; on the contrary, it clarifies various aspects of the present invention while the object and scope thereof are defined by the scope of protection of the appended claims.

Before proceeding with the detailed description of the method according to the invention, it is necessary to understand the structure and operation of the electromechanical apparatus in which the method is implemented. In particular, an apparatus operating according to EBM technology and intended to manufacture three-dimensional products from metal powders and using a focused electron beam according to the principles of additive manufacturing technologies is described hereinafter by way of example.

With particular reference to Figure 1, reference number 1 illustrates overall and schematically the structure of an EBM apparatus for the production of three-dimensional objects starting from computerized 3D models. In the specific case, it is an additive manufacturing system using Electron Beam Melting (EBM) technology. The apparatus 1 deals particularly, but not exclusively, with metal powders such as titanium powders or alloys thereof, such as Ti6Al4V.

It should be noted that the metallic material of the powder does not in any way represent a limitation of the Applicant's rights, as well as of the scope of application (biomedical, aerospace, etc.) of the objects obtained through the EBM process.

The EBM apparatus 1 comprises a programmable electronic unit 100 for command and control of the operational steps of the production process. The electronic unit 100 is conventionally provided with user interfaces such as a keyboard and a display, not shown in the drawings to the extent that they are conventional. The unit 100 is also provided with a data processing board provided with an electronic controller in bi-directional communication with a memory bank which may be on board the board itself or otherwise associated with or in communication with the command and control unit 100.

Control buttons are also provided for direct regulation of some functions of the apparatus 1, such as the start or restart step, or for forcing predetermined operational regulation steps of the production cycle.

The high voltage means HV 12 are connected to the electronic unit 100 for the generation of pulses for emission of an electron beam, schematized in the figures with the reference number 3.

The electron beam 3 is generated within an electron gun 2 which, similar to a cathode ray tube, receives incoming high voltage pulses from the generating means 12 and produces the electron beam 3 directed towards a work plane 6.

More specifically, the electron beam 3 is emitted by an electron generating system incorporating a crystal element or an incandescent tungsten filament (not shown in the figure). In either case, this system is fed by a high electric potential or by a current which activates the generating means 12. A nozzle (not shown in the figure) placed beneath the crystal element shapes the beam and directs it towards the working plane 6.

Inside the electron gun 2 there are some electromagnetic coils 4 which in turn are connected to the electronic unit 100 which commands and controls the energization of the same to deflect or, better, regulate the direction of the electron beam 3. In fact, in order to obtain the desired geometries of the products, the electron beam 3 must be appropriately moved and modulated using the electromagnetic coils 4 which deflect it to the point of impact.

The apparatus 1 comprises a processing chamber 5 within which the free end of the barrel 2 terminates, above the working plane 6.

Overall, since the electron beam 3 must be generated in a high vacuum to avoid phenomena of interaction of the electrons with molecules in the atmosphere, the EBM apparatus 1 further comprises vacuum control means 8.

The chamber 5 comprises the reservoirs 7 and 9 of the metal powders 10 which are preferably arranged on opposite sides with respect to the work plane 6. A collecting/distributing device 11, i.e. a device intended to collect and distribute the correct quantity of powder 10, is provided in a sliding manner along the work plane 6 to obtain a uniform layer for the melting step.

Three-dimensional fusion-sintered objects or products are manufactured on the work plane 6 from the metal powders 19 contained in the tanks 7, 9.

Such powders 10 are collected and distributed by the device 11 in order to obtain a layer to be melted which is always uniform. A level shifter 13 is associated with the work planes 6 to regulate the development and manufacture of the products through upward or downward movements along the vertical axis Y, considering that the work plane is located in a horizontal plane X.

The command and control unit 100 includes a hardware and software component interface intended to manage the entire EBM process, as well as the steps of the method of the present invention and the signals from the various sensors.

The interface software ensures the integration and operation of all the component parts of the apparatus 1 by means of the regulation and initial adjustment of a composition of machine instructions which is hereinafter also referred to as “theme”, this term being understood as the set or package of information containing the management parameters of the electron beam 3 which regulate the generation and impact energy according to the operations to be performed.

The electronic unit 100 also manages the vacuum control means 8 which regulate the vacuum level inside the chamber 5 by the controlled introduction of small quantities of inert gas.

The method of the present invention for regulating the operation of the EBM apparatus 1, in order to obtain certified processed products, will now be described in detail.

In its most general form, the method in question includes the following steps:

1) an IQ calibration procedure: which verifies the correct operation of all the component parts of the device necessary to ensure its full functionality;

2) an operational qualification procedure OQ: which verifies the operational efficiency of the melting process itself in order to define the adjustment limits of the apparatus itself;

3) a performance qualification (PQ) procedure: which verifies the stability and repeatability of the process within a predetermined process window.

Figure 2 shows a summarized block diagram of these steps, which exemplifies the evolution of the steps of the EBM process that allows obtaining pieces of any shape and geometry from an adequate preparation of an .abf file related to the composition or theme to be developed.

Let us now look in more detail at the peculiar aspects of these procedures.

Step 1) IQ Calibration Procedure

An EBM process carried out within an EBM melting apparatus uses different files, hardware parameters and software parameters depending on the type of metal powder used, for example Ti Gr.2 or Ti6Al4V. In order to realise the production programs carried out on the different types of apparatus available, reference is made to a series of operating instructions defined together with the apparatus manufacturer.

In essence, an IQ calibration procedure is based on verifying that the hardware and software components of the device 1 are present and functioning, as well as that all surrounding conditions are met, if necessary (e.g. environmental conditions, safety conditions, verification of any auxiliary units, calibration, etc.).

More particularly, with the initial calibration procedure, the functionality of the most important component parts of the apparatus 1 is verified by means of sensors and/or measuring instruments present on the apparatus itself. Furthermore, the verification of the EBM process parameters takes place according to the worst-case analysis criterion, defining and evaluating the characteristics of the product/process in the worst operating case identified and for each apparatus supplied and for each material used by it.

For example: in order to verify the correct functionality of the main component parts of the device 1 and the moving elements, the following check must be made:

- the vacuum condition of the working chamber 5 can be detected by means of pressure sensors;

- the temperature of the work surface 6 and the process environment can be detected by means of temperature sensors;

- the current applied to the filament of the electron gun 2 is easily detectable by means of a current sensor;

- the movement of the moving component parts, such as the distributor device 11 and the work plane shifter 13, is detected by means of position sensors.

The calibration of the vacuum sensors is checked by means of suitable certified reference instruments; while the movement of the distribution device 11 and the displacer 13 is regulated so that the distribution of the powder layers is uniform and constant for each of the layers manufactured.

In particular, calibrations should be performed in order to verify that the HW components of the EBM process are correctly calibrated, and that consequently the values read on the SW interface are true.

Thermocouple calibration verification shall be done with appropriate calibration probes connected to the thermocouple wire placed in contact with the starter plate. Vacuum sensor calibration verification shall be done by connecting a calibration probe, through suitable connections, along the main line of the turbo pumps connected to the barrel and the EBM chamber and the backup pump connected to the EBM chamber.

HV calibration verification should be done using a calibrated voltmeter and properly connecting an adapter to the appropriate contact terminals. The test execution mode and the readings made should be as stated in the reference specification. Calibration of the start plate movement should be verified by lowering the plate using the software interface and checking that the lowering level corresponds to the preset level.

By doing so, it can be demonstrated that the actual configuration of the machine corresponds to the ideal operating conditions stated by the manufacturer of the apparatus 1.

Also, the electron beam 3 is suitably calibrated to be focused on the working plane 6.

Ideal conditions can be identified in a series of parameters or reference values that are part of both the equipment assets based on the technical specifications provided by the manufacturer, and information derived from historical series of processes already carried out that have allowed the collection of data and statistical series on the configuration of the device and related results of the processes carried out.

These data and reference information are contained in the memory bank 12 associated with the command and control unit 100. Optionally, documentary review of the presence of all the components of the apparatus 1 specified by the supplier is also provided as well as documentation relating to the verification of the correct assembly of the machine, to ensure, at least after the first installation, that the functionality of the machine complies with the sales specifications.

In summary, the minimum tests to be performed in the calibration step are shown in the following table:

With these tests, it is now possible to collect a set of data and values of some parameters that affect the correct performance of the subsequent fusion process. These data and values, possibly retrieved in the form of a range of values, are stored in the memory bank associated with the electronic command and control unit 100. Step 2) Operational qualification procedure OQ

The operational qualification procedure aims at finding a process window within which EBM fusion is considered optimal. In other words, it aims at identifying ranges of values of process parameters within which fusion products are considered to be of good quality.

The parameters of the composition or theme process are changed forcefully to achieve the maximum and minimum energy levels that allow for correct fusion of the powders.

For each of these two extreme configurations, or better, the extremes of the range of values in the process parameters, corresponding samples or specimens are made, which are subsequently characterized and tested to ensure that under extreme conditions of use of the system, the manufactured products will meet the established minimum requirements. Hereafter, example A and example B refer to the relevant results of the fusion process under extreme conditions of minimum level (A = Low Energy) and maximum level (B = High Energy) of the fusion energy.

The process in example A is used to check the parameters that have the greatest impact on the quality of the manufactured products, while the process in example B verifies the parameters that are less important, such as those that regulate the passage of the electron beam in limited areas or that correct inaccuracies in the same.

The acceptability requirements for each test are established according to international regulations, if they exist, or on the basis of a historical listing of data and experience from previous activities carried out by the Applicant, if the regulations are deficient.

Still as an example, coded tests are performed at the beginning by identifying the parameters with the greatest impact, and identifying their contribution to the energy balance.

The two settings of these parameters that identify the minimum and maximum energy released during the melting process are tested in a sequence. In addition, aspects related to the operations of the apparatus 1, such as for example the quality of the powders, the performance of the high voltage unit, the correct calibration of the electron beam, the movement of the displacer device and the work plane, are covered by specific and individual tests.

In order to apply the operational qualification procedure OQ according to the method of the present invention, it was necessary to identify the critical parameters and distinguish them from those that are not critical, according to some principles described hereinafter.

First of all, it should be considered that the method of the present invention assumes that the electromechanical apparatus 1 under consideration in this case is an EBM apparatus, which carries out a melting process based on a heat equilibrium law.

In fact, the vacuum and heating conditions of the powder require the observance of an equivalence principle between the heat released by the electron beam and the heat dissipated through the material.

This normally results in the setting of an average electron beam power such as to ensure a correct balance of these quantities, expressed in terms of current required to generate the electron beam and used for the various melting operations, which can be distinguished into: heating; melting of solid parts, melting of contours and porous structures, or also any intermediate heating step, always to ensure the correct heat balance.

Figure 3 schematically shows a diagram of the compensated thermal equilibrium operating principle involved.

More particularly, this principle must ensure thermal equilibrium for a total volume of solid made of any shape and size. Furthermore, in order to identify the critical parameters, each parameter of the calibration parameter group has been evaluated for the impact it has on the process and on the final features of the products obtained by fusion.

As is clear from Figure 3 above, the process proceeds with an alternation of heating and cooling steps affecting predetermined parts of the products to be manufactured. In any case, the overall equilibrium is almost perfectly equivalent.

As explained above, the EBM process bases its operation on the creation of an electron beam 3 to fuse the metal powders. The electrons are focused and moved through the use of magnetic coils 4 located on the sides of the gun 2 which transports the electron beam into the fusion processing chamber or EBM 5.

In order to achieve the desired geometry of the products, beam 3 must be moved appropriately and its energy modulated to allow an adequate transfer of energy to the powder, to melt it and maintain constant the temperature of the molten layer, to make uniform components from the structural point of view (density) and physical-chemical-mechanical properties.

This process is achieved through the use of a SW application and HW components, specifically:

- movement of the device 11 responsible for collecting and distributing the correct quantity of powder, in order to obtain a uniform layer to be melted. The measurement of the quantity of powder distributed is controlled by reading two sensors placed on the sides of the work surface 6.

- filament current of gun 2, which is linked to the energy of the electrons and which is regulated according to the operations performed by beam 3 (consisting, for each powder layer melting process, of: powder heating (a), and melting of contours (b), solid parts (c) and network structures (d), in this order). - electron beam management parameters, contained in the information package called “Tema” within the EBM control software application. The Tema is divided by process steps (preheating, contour melting and network) and controls the energy that the electron beam must have in order to optimize the melting process of the manufactured components, in terms of beam 3 and current pass rate.

Therefore, the parameters that can strongly influence the process will be related to these aspects of the electron beam 3.

In order to further optimize the fusion process to allow maximum flexibility to the system in terms of achievable geometries, parameter sets have been provided that improve the behavior of the electron beam locally, enhancing and refining the passing speed in certain areas and to make particular geometries.

These parameters have a lesser impact on the process, in terms of the final characteristics of the manufactured product. Therefore, it is decided to divide the parameters of the subject into critical and non-critical ones, and to provide the identification of the intervals of use and tests for the former to check the quality of the process over the entire interval identified in this way, and for the latter a verification test of the optimization made to the process.

The critical parameter ranges were determined experimentally based on the experience and know-how acquired over the years by the Applicant, in particular in the manufacture of prosthetic components using EBM technology.

Advantageously, according to the invention, it was possible to determine that each of the parameters identified as key to the process affects the amount of energy delivered by the electron beam 3 and this has a direct impact on the characteristics of the products obtained by sintering and on their uniformity. Indeed, detailed studies undertaken during the development of the apparatus and the method according to the invention made it possible to determine that the energy of the beam 3, under equal environmental conditions (vacuum and other initial conditions), is responsible for the temperature level of the molten layer.

For each EBM composition or fusion theme, some equations were developed that quantify the energy of the electron beam used, based on the following principles:

where:

T is the temperature of the molten layer;

E is the energy applied to the electron beam;

A is the fusion area;

t is the fusion time;

I is the electron beam correlation filament current; and

V the potential across the filament.

For example, depending on the type of subject matter to be made, i.e. depending on the type of products that need to be manufactured, the control unit 100 of the apparatus 1 is capable of calculating, by means of an automated procedure, the type of energy to be imparted to the electron beam for a correct and efficient production of certified processed products. In doing so, the control unit uses correlation formulas between the voltage applied to the terminals of the electron gun 2, the filament current, the duration of exposure to the beam and the temperature of the molten layer.

Still as an example only, the following correlation formula is used for the preheating step

Other correlation formulas are used for the other actual body melting steps of the products or contour melting or lattice curing.

It should be noted that if one parameter of the correlation formula is modified, it is also appropriate to modify others to compensate for it. However, in this way it is also possible to define the extreme limits of the variation of the parameters by identifying a range of multiple values within which most of the processes to be carried out are applicable.

For example, by varying the above parameters between the maximum and minimum values of a predetermined range, it is possible to obtain a minimum fusion energy level (example A) and a maximum fusion energy level (example B) applied by the electron beam on the powder layer. The ranges of use of the critical parameters are given in the following table:

In practice, the procedure consists of preparing the EBM apparatus according to the specifications and the IQ calibration procedure. The parameters of the subject to be made are set to the values shown in the “example A” configuration. In a second and subsequent processing step, the parameters are set to the values indicated in the “example B” configuration.

The products obtained as a result of these configurations are subjected to a series of quality tests to verify that the results of the production steps are consistent with the values indicated by the reference standards and recorded in the dedicated locations of the memory bank associated with the control unit 100 of the apparatus. This final control step will be described in more detail with reference to the third performance qualification step.

These quality tests are:

- Proof of the dimensional correspondence L;

- Tensile tests in the z direction;

- Tensile tests in the x and y directions;

- Complete chemical analysis;

- Evaluation of porosity, discontinuities or micrography;

- Visual, adhesive and compression analysis of the structural network.

Quality tests are carried out according to predetermined specifications which also include the methods and patterns of cutting the resulting samples, the heights of the cuts made and all sizes of blocks subjected to tension or compression.

Specimens and samples are distributed in such a way as to provide an indication of the entire production volume possible in the EBM apparatus under examination. The validity of the intervals in the parameter values is verified by carrying out a specific test.

To summarize what is set forth herein, a table is provided below listing the critical parameters by type of material used (for heating and melting operations of solid parts, contours and porous structures, respectively). The table also shows the effects resulting from incorrect setting of these parameters. As a result of the tests carried out, it is possible to define the validity intervals of all parameters.

Step 3) PQ Performance Rating Procedure

The final PQ procedure is based on the verification of the configuration of the process parameters and the confirmation of their capacity, based on pre-established acceptability criteria.

Therefore, this PQ procedure should verify that the EBM process has been able to produce cast components having features that meet the provisions of the acceptability criteria in a stable and repeatable manner.

To do so, quality controls are carried out on samples of the products obtained.

Such controls may be by sampling or on the first production batches, for example, the first three batches, or even on all batches in the case of limited series and high quality productions. Of course, the choice of the type of sampling depends on various factors that do not fall within the principles of the present invention and therefore the description of them will be omitted to avoid obstructing the following.

Since the EBM process bases its operation mainly on the creation of an electron beam to melt the metal powders, it is established to evaluate the final characteristics of the melted powders in order to verify the production stability of the process for a number of processes equal to at least three, which represents a minimum guarantee of repeatability of the melting operations.

Critical parameters regulate the characteristics of the electron beam and determine the amount of energy E released onto the powder layer (and consequently the required generation current and electron beam velocity). There are also non-critical parameters that refine the electron beam path to allow for different geometries to be realized, even within a single processing step.

By acting on functions that modulate the electron beam according to the length of the lines to be fused, the distance from the part contour and the presence or not of a fused layer on the underlying layers, all factors read directly from the .abf file loaded at the beginning of the processing step (see Figure 2), non-critical parameters are used to maintain the same electron beam efficiency in any area of the build volume and for any geometry made.

Furthermore, since the operation of the EBM system has been verified by means of the OQ procedure within a well-defined process window, the tests provided by the PQ procedure are carried out on material produced using process parameters that fall within the previous field of use of the apparatus and can be verified by monitoring them.

Again for illustration purposes, seven tests were developed to be run for the first three consecutive production processes (regardless of size but pertaining to products that can be manufactured).

Well, according to the method of the present invention, if the results of the tests or the various tests are within the limits, the process is considered under control and the related products are considered to comply with the specifications and are therefore certified.

Otherwise, a corrective action is activated in order to bring the process back to ideal operating conditions, compensating for all drifts.

Advantageously, the regulation intervention on the generation energy E of the beam 3 of the EBM apparatus makes it possible to quickly remedy more than one deviation affecting more than one parameter. Operationally, the regulation of said generation energy of the electron beam 3 is carried out by regulating the current applied to the filament of an electron beam generation gun 2 itself.

In essence, beam generation energy regulation E is a correction applied to a single parameter against the deviation of one or more process parameters.

Any correction or corrective compensation of process drifts is carried out by changing a single related parameter which, in this case, is represented by the application energy of the electron beam of the EBM apparatus.

Other optional actions may be taken, such as:

- new laboratory tests to confirm the actual crossing of the acceptability limits;

- checking some hardware parts of the device;

- verification of calibration of critical process parameters;

- verification of the correct application of the procedures/instructions for execution/control of the process (for example: process execution, process control and staff training);

- increase the frequency of monitoring critical process parameters to determine their stability over time.

Claims (8)

CLAIMS 1. Method for regulating the operation of an EBM apparatus (1) to obtain certified processed products, the method comprising: an initial calibration step to check the correct operation of all component parts of the EBM apparatus (1) and structured to ensure full functionality thereof; and a subsequent quality control step carried out on the obtained products that are obtained by the work process carried out; the method comprising: - defining a plurality of measurement parameters in relation to the component parts of the EBM apparatus (1); - measuring said measurement parameters by means of sensors and/or measurement indicators coupled to an apparatus control unit (100) and related to said measurement parameters during at least one processing phase performed by said EBM apparatus (1); - performing a quality control step on the products obtained after the work process, and obtaining quality data related to any deviation from the expected quality, wherein said quality control step provides a predefined series of dimensional, chemical-physical and strength checks, and wherein said quality control step provides at least the following tests on samples of the products obtained: - Testing about dimensional correspondence L; - Tensile tests in the z direction; - Tensile tests in the x and y directions; - Full chemical analysis; - Evaluation of porosity, discontinuities or micrography; - Visual, adhesive and compression analysis of the structural network; - comparing said measured parameters and quality data with the corresponding reference parameter values available for that specific EBM apparatus (1) and for the type of products obtained; - detecting any deviation in one or more of said measured parameters or said quality data with respect to the reference parameter values; - calculating, on the basis of such deviations, a total correction and regulation value of an electron beam generation energy (3) of said EBM apparatus (1); - applying said total correction and regulation value to the electron beam generation energy (3) of said EBM apparatus (1); the electron beam generation energy (3) being obtained from correlation formulas between the parameters associated with the component parts of the EBM apparatus (1) based on the following relationships: E°c t -I V wherein: T is the temperature of the molten layer; E is the energy applied to the electron beam; A is the melting area; t is the melting time; I is the current of the electron beam generating filament; and V is the potential across the filament; wherein the control unit (100) of the apparatus (1) calculates the total correction and regulation value on the basis of said correlation formulas, and automatically applies the total correction and regulation value to the electron beam generating energy (3) to make processed products corresponding to a predetermined quality level; wherein the step of defining the plurality of measurement parameters in relation to the component parts of the EBM apparatus (1) is modified during the progress of the useful life of the EBM apparatus (1) and also after the application of said total correction and regulation value; and wherein the regulation of said electron beam generation energy (3) is provided by adjusting an electric potential and/or current applied to a system for generating said electron beam (3). 2. Method according to claim 1, characterized in that a drift of only one parameter relative to a mechanical structural part of the EBM apparatus (1) provides a correction and adjustment of that single mechanical structural part. 3. Method according to claim 1, characterized in that the phase of measuring said parameters is carried out by means of sensors and/or measurement indicators mounted on the same EBM apparatus (1). 4. Method according to claim 1, characterized in that the measurements of said parameters and the values of the reference parameters are stored in a memory part associated with the apparatus control unit (100). 5. Method according to claim 1, characterized in that the initial calibration step establishes operating parameters in a predetermined range between a series of maximum and minimum values. 6. Method according to claim 1, characterized in that said quality control step on the products obtained is regulated by sampling at a fixed rate or on the first production batches of said products obtained. 7. EBM apparatus (1) structured to obtain certified processed products by implementing a method for regulating the operation according to any of claims 1 to 6. 8. EBM apparatus according to claim 7, comprising a system for generating an electron beam (3).